Dual-wavelength UV degradation of bisphenol A and bezafibrate in aqueous solution using excilamps (222, 282 nm) and LED (365 nm): yes or no synergy?

Dual-wavelength ultraviolet (DWUV) irradiation can lead to a synergistic effect in terms of accelerated degradation of emerging organic contaminants in aqueous media. This study compared the kinetics of single-wavelength and DWUV degradation of bisphenol A (BPA) and bezafibrate (BZF) in model aqueous solution using KrCl (222 nm), XeBr (282 nm) excilamps and LED (365 nm). Three novel dual combinations (222 + 282, 222 + 365 and 282 + 365 nm) were examined toward the potential synergy in direct photolysis and advanced oxidation processes (AOPs) using potassium persulfate and hydrogen peroxide. Kinetic comparison showed that the time- and fluence-based synergy did not occur in the dual combinations selected. Meanwhile, the single-wavelength UV treatment using KrCl excilamp was found to be highly efficient for degradation of target contaminants. At a given dosage of oxidants, the UV/S2O82- process exhibited higher performance than the UV/H2O2 one, attaining higher degradation rates and requiring lower UV fluences for 90% removal. This study demonstrates that the catalyst-free UV/S2O82- process using KrCl excilamp has a high potential for efficient removal of such organic contaminants from real waters with low turbidity.

E-Z Isomerization Mechanism of the Green Fluorescent Protein Chromophore: Remote Regulation by Proton Dissociation of the Phenol Group.

Dronpa, a GFP (green fluorescent protein)-like fluorescent protein, allows its fluorescent and nonfluorescent states to be switched to each other reversibly by light or heat through E-Z isomerization of the GFP chromophore. In this article, a GFP chromophore (p-HBDI) in water is used as a model to explore this E-Z isomerization mechanism. Based on the experimental solvent isotope effect (kH2O/kD2O = 2.30), the E-Z isomerization of p-HBDI in water is suggested to go through the remote-proton-dissociation-regulated direct mechanism with a proton transfer in the rate-determining step. The fractionation factor (ϕ) of the water-associated phenol proton of p-HBDI in the transition state is found to be 0.43, which is exactly in the range of 0.1-0.6 for the fractionation factor (ϕ) of the transferring proton in the transition state of R2O···H···O+H2 in water. This means that the phenol proton of E-p-HBDI in the transition state is on the way to the associated water oxygen during the E-Z isomerization. The proton dissociation from the phenol group of p-HBDI remotely regulates its E-Z isomerization. Less proton dissociation from the phenol group (pKa = 8.0) at pH = 1-4 results in a modest reduction in the E-Z isomerization rate of p-HBDI, while complete proton dissociation from the phenol group at pH = 11-12 also reduces its E-Z isomerization rate by one order of magnitude because of the larger charge separation in the transition state of the p-HBDI anion. All of these results are consistent with the remote-proton-dissociation-regulated direct mechanism but against the water-assisted addition/elimination mechanism.

Ultrasound Treatment of Buckwheat Grains Impacts Important Functional Properties of Resulting Flour.

The benefit of not containing the gluten complex protein also provides problems with the achievement of typical and proper texture, especially in bakery products. Ultrasound (US) treatment has been previously studied on buckwheat as assistance treatment facilitating the release of antioxidant compounds. However, there is no study regarding the changes occurring in US-treated buckwheat grains regarding the structure-creating capacity, like water absorption, gelling, and pasting. The aim of this study is to the impact of US-treatment of buckwheat grains at 1:10, 1:5, and 1:2.5 solid: liquid ratio (in water). The particle size distribution, water absorption index (WAI), water solubility index (WSI), swelling power (SP), pasting characteristics, color, soluble, insoluble and total polyphenols content (SPC, IPC, TPC) and antioxidant activity (DPPH) were assessed in resulting flours. US-treatment caused specific agglomeration, resulting in bigger particles for 1:5, and 1:2.5 ratio treated samples, while higher dilution (1:10) increased smaller particle size fractions. The WAI and SP were the highest for the1:5 solid: liquid ratio sample, and the same sample revealed the highest peak viscosity, breakdown, and setback values. The ultrasound treatment increased the WSI, which was positively correlated with insoluble polyphenols content. The soluble polyphenols content decreased, and insoluble polyphenols content increased in all ultrasound treated samples. The DPPH scavenging activity remaining in grain after US treatment was lowered compared to the control sample. The relocation of pigments resulted in a redness and yellowish increase in all treated samples, while lightness was also increased but was most pronounced for a 1:10 ratio treated sample. The results suggest that ultrasound treatment of grain can improve the essential functional properties of buckwheat flour.

Enhancing the performance of pollution degradation through secondary self-assembled composite supramolecular heterojunction photocatalyst BiOCl/PDI under visible light irradiation.

A novel n-n type inorganic/organic heterojunction of flaky-like BiOCl/PDI photocatalyst was constructed by water bath heating method. Meanwhile, a simple method - secondary self-assembly was used to prepare the BiOCl/PDI with a special band structure. The photocatalytic activities were evaluated by degrading aqueous organic pollutants under visible light (λ > 420 nm). The removal rates of 5 mg L-1 phenol (non-ionic type), methyl orange (MO, anionic type), rhodamine B (RhB, cationic type) and 10 mg L-1 RhB by secondary self-assembly BiOCl/PDI (BiOCl/PDI-2) were 8.0%, 3.4%, 27.8% and 78.9% higher than self-assembly BiOCl/PDI (BiOCl/PDI-1) under visible light (λ > 420 nm). The better photocatalytic activity for BiOCl/PDI-2 was attributed to the optimization of energy-band structures, which arose from different exposed surfaces, narrower interplanar spacing and stronger visible light absorption performance. Under acidic condition, BiOCl/PDI-2 showed a good photocatalytic activity, which was not affected by neutral ionic intensity and had good recycling properties. Moreover, the photocatalytic mechanism was explored by free radical capture test and electron paramagnetic resonance (EPR), and contribution of active species was calculated. The main active species of BiOCl/PDI-2 were ·O2-, 1O2 and h+. Our work may provide a route to design efficient inorganic/organic heterojunctions for organic pollutants degradation.

Two novel MOFs@COFs hybrid-based photocatalytic platforms coupling with sulfate radical-involved advanced oxidation processes for enhanced degradation of bisphenol A.

Nowadays, the visible-light-driven photocatalysis via advanced photocatalyst for PS activation have promising applications in wastewater treatment. Herein, for the first time, two novel MOFs@COFs hybrid materials (denoted as MIL-101-NH2@TpMA and UiO-66-NH2@TpMA) with nitrogen-rich building blocks were fabricated via a feasible step-by-step assembly method, and then employed as efficient photocatalytic platform coupling with sulfate radical-based advanced oxidation processes for the degradation of BPA under visible light irradiation. Detailed analyses revealed that the hybridization of MOFs and COFs could greatly boost visible light absorption, while the heterojunction formed at the interface could effectively facilitate the separation and transfer of photogenerated electron-hole pairs. More importantly, the developed solar/MOFs@COFs/PS system exhibited the excellent degradation ability toward BPA, and an incredible degradation efficiency of 99% was eventually achieved. Possible mechanism for photocatalytic degradation of BPA was also proposed. Furthermore, the prepared composites with great reusability and stability possessed a broad potential for highly effective degradation of various organic contaminants. In short, this work not only demonstrated the combination of MOFs and COFs with C3N4 active unit was a feasible strategy for improving photocatalytic activities in the degradation of organic contaminants, but also provided some novel inspirations for constructing high-efficient photocatalysts with heterostructure.

Impacts of sulfidation of silver nanowires on the degradation of bisphenol A in water.

Silver nanowires (AgNWs) are widely produced in many electronic and optical products, and could be inevitably discharged into the aquatic environments. Sulfidation is one of the most important transformation processes of AgNWs, and could significantly affect their fate and interactions with other pollutants in aquatic environment. In the present study, the sulfidation products of AgNWs with different atomic ratio of Ag and S were prepared under environmentally relevant conditions. The crystal structure, elemental composition, morphology and size of the sulfidation products were comprehensively characterized by powder X-ray diffraction, UV-vis spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscope. The products were heterostructured nanowires and the Ag2S/Ag molar ratio increased with extension of the reaction time. The produced Ag2S-Ag nanowires displayed a good photocatalytic activity and facilitated the degradation of the copresent organic pollutant bisphenol A (BPA) under simulated sunlight irradiation. As sulfidation time increased, more Ag2S was generated and the Ag2S-Ag composites displayed high promotion effect on BPA degradation. This effect could be ascribed to the favorable synergistic effects between Ag2S and AgNWs, such as high electron-hole separation efficiency and low charge transfer resistance. The chemical scavenger experiments demonstrated that superoxide anion radicals and photogenerated holes in the sulfidation products of AgNWs could be the main reactive species for photocatalytic degradation.

Utilization of activated carbon for maximizing the efficiency of zirconium oxide for photodegradation of 4-octylphenol.

Utilization of AC/zirconium oxide (ZrO2) for the removal of 4-octylphenol (4-OP) from aqueous solution has been studied under simulated visible-light as a cost effective technique. To draw complete images for the prepared materials, a series of characterization methods was performed. Brunauer-Emmett-Teller (BET) data has proved that AC has high surface area and total pore volumes that are decreased after incorporation of ZrO2. Morphologically, TEM showed massive quantity of ZrO2 spherical shape nanoparticles loaded with carbon and EDX showed the uniform distribution of all the prepared materials. The photocatalytic performance has been traced via adopting a matrix effect analysis to correlate the photodegradation of 4-OP in the presence of visible light as a time function, pH, photocatalyst dose and initial concentration of 4-OP. The positive impact of AC content in AC/ZrO2 composite on the adsorption of 4-OP was strikingly observed with expanding the AC content in AC/ZrO2 composite up to 33% (wt/wt). Almost 97% of the 4-OP was removed within 180 min under simulated visible light. The optimum reaction conditions for 95% removal of 4-OP were 120 min, 1 g L-1 catalyst dose at pH 8. The photocatalytic degradation of the 4-OP was well fitted with pseudo first-order L-H kinetic model.

Natural sunlight-driven aquatic toxicity enhancement of 2,6-di-tert-butylphenol toward Photobacterium phosphoreum.

The tert-butylphenols (TBPs) are one group of alkylated phenolic compounds with wide applications in UV absorbers and antioxidants. They are becoming contaminants of emerging concern with residues frequently detected in natural surface water or drinking water. The direct sunlight may photolyze TBPs in waters and affect their aquatic toxicities; however, such data are very limited. In the present study, we investigate the photodegradation of 2,6-DTBP by direct sunlight in water and compare the aquatic toxicities of 2,6-DTBP with that of its product toward Photobacterium phosphoreum. 2,6-DTBP is photodegraded by 71.31 ±â€¯2.64% under simulated sunlight following a pseudo-first-order kinetics with rate constant (k) of 0.061 h-1. Density functional theory simulations at M06-2X/def2-SVP level reveal that the photodegradation occurred sequentially through oxidation, photo-isomerization and hydrogenation. The degradation product 2,5-DTBP is toxic to P. phosphoreum (EC50 3.389 × 10-5 mol/L) whereas 2,6-DTBP is not harmful (EC50 3.917 × 10-3 mol/L) as designated by the European Union Standard, indicating the enhanced toxicities driven by the direct sunlight photodegradation. We demonstrate the enhanced toxicities of 2,6-DTBP by natural sunlight, suggesting that negligence of photodegradation of TBPs-related contaminants will underestimate the comprehensive risk of these emerging contaminant in natural waters.

Photocatalytic treatment of organic pollutants in a synthetic wastewater using UV light and combinations of TiO2, H2O2 and Fe(III).

In this study, the photocatalytic treatment of an organic wastewater with/without phenolic compounds by means of ultraviolet irradiation, titanium dioxide and hydrogen peroxide was examined in an annular photoreactor. Specifically, the effect of initial total carbon concentration, catalyst loading and H2O2 amount on the removal of total carbon was first examined in the case of a synthetic organic wastewater. The influence of partial carbon substitution by phenol, 2-chlorophenol, 2,4-discholophenol, trichlorophenol, and 4-nitrophenol on total carbon removal and target compounds' conversion was studied keeping constant the initial organic carbon load. It was shown that the process applied was effective in treating the wastewater for initial total carbon 32 mg L-1, 0.5 g L-1 TiO2, and 66.6 mg L-1 H2O2. Applying UV/TiO2 and UV/H2O2, 58% and 53% total carbon removals were achieved, respectively, but combining TiO2 and H2O2 did not result in a better performance in the case of the synthetic wastewater without any phenolic compounds. In contrast, when a phenolic compound was added, the addition of H2O2 was beneficial, eliminating the differences observed from one phenolic compound to another. The total carbon removals observed were lower than the corresponding final conversions of the target phenolic compounds. Finally, the electric energy per order values were calculated and found to range in 52-248 kWh/m3/order, being dependent from the process applied and the phenolic compound present in the wastewater.

Degradation of bisphenol a using peroxymonosulfate activated by WO3@MoS2/Ag hollow nanotubes photocatalyst.

WO3@MoS2/Ag (HW@MA) hollow tubes were successfully engineered to photodegrade bisphenol A (BPA) combined with peroxymonosulfate (PMS) for the first time. XRD, XPS, TEM and SEM were conducted. The HW@MA tubes present excellent photocatalytic performance on the removal of BPA. The intermediate products of BPA were investigated by GC-MS analysis and the degradation pathway was proposed. To explore the transferred mechanism of photoproduced carriers, the electron paramagnetic resonance (EPR) technique was carried out. The results revealed that the superoxide radical (O2-), hydroxyl radical (OH), sulfate radical (SO4-) were the main active radicals. Moreover, the formed schottky junctions enhanced the separation efficiency of photoinduced electron-hole pairs. Besides, the effect of the photocatalysts' dosage, PMS concentration, pH of the initial solution and co-existing anions on the BPA degradation were investigated.

Monitoring mitochondrial pH with a hemicyanine-based ratiometric fluorescent probe.

Mitochondria as essential organelles play critical roles in cellular metabolism. Mitochondrial pH is a vital parameter that directly affects the unique function of mitochondria. Herein, we present a new ratiometric fluorescent probe M-pH for monitoring the pH within the mitochondria. M-pH consists of a stable and large π-electron conjugated merocyanine system. The lipophilic cationic benzyl group will facilitate the accumulation of M-pH in mitochondria. The phenol unit is the recognition moiety, achieving the ratiometric sensing of pH changes. The experimental results indicate that M-pH displays ratiometric fluorescence response to different pH values. Meanwhile, M-pH shows negligible response to common species, and has high stability and low cytotoxicity. In biological experiments, M-pH can solely accumulate in mitochondria and visualize the pH changes during mitophagy and cell apoptosis. We thus believe that M-pH has great potential as a practical tool for real-time monitoring of pH changes of mitochondria, contributing to revealing the pathogenesis of mitochondrial pH associated diseases.

Excellent Temperature-Control Based on Reversible Thermochromic Materials for Light-Driven Phase Change Materials System.

Light-driven phase change materials (PCMs) have received significant attention due to their capacity to convert visible light into thermal energy, storing it as latent heat. However, continuous photo-thermal conversion can cause the PCMs to reach high thermal equilibrium temperatures after phase transition. In our study, a novel light-driven phase change material system with temperature-control properties was constructed using a thermochromic compound. Thermochromic phase change materials (TC-PCMs) were prepared by introducing 2-anilino-6-dibutylamino-3-methylfluoran (ODB-2) and bisphenol A (BPA) into 1-hexadecanol (1-HD) in various proportions. Photo-thermal conversion performance was investigated with solar radiation (low power of 0.09 W/cm2) and a xenon lamp (at a high power of 0.14 W/cm2). The TC-PCMs showed a low equilibrium temperature due to variations in absorbance. Specifically, the temperature of TC-PCM180 (ODB-2, bisphenol A and 1-HD ratio 1:2:180) could stabilize at 54 °C approximately. TC-PCMs exhibited reversibility and repeatability after 20 irradiation and cooling cycles.

Dragon's Blood Sap: Storage Stability and Antioxidant Activity.

Currently, consumers are demanding additive-free, fresher, and more-natural products. Dragon's Blood Sap (DBS), the deep red latex of the specie of tree Croton lechleri (Müll. Arg.), contains a high concentration of phenolic compounds of great interest for the food, pharmaceutical, and cosmetic industries. These chemical compounds are highly susceptible to degradation. Therefore, DBS storage stability and its photo-oxidation was studied by Fourier transform infrared spectroscopy (FT-IR) and UV-Vis spectrophotometry for 39 days at different temperatures (4⁻21 °C) and relative humidities (0⁻56%), as well as under UV light exposure. It was observed that the degradation of phenolic compounds was reduced at 0% relative humidity (RH), not showing a significant effect of temperature in the range studied. UV light irradiation degraded DBS in a 20%. DBS has an exceptional high and stable antioxidant content (≥93% inhibition percentage of DPPH), which makes it a unique property to consider the DBS as an antioxidant agent or ingredient for consumer products formulations.

Activationless Multiple-Site Concerted Proton-Electron Tunneling.

The transfer of protons and electrons is key to energy conversion and storage, from photosynthesis to fuel cells. Increased understanding and control of these processes are needed. A new anthracene-phenol-pyridine molecular triad was designed to undergo fast photoinduced multiple-site concerted proton-electron transfer (MS-CPET), with the phenol moiety transferring an electron to the photoexcited anthracene and a proton to the pyridine. Fluorescence quenching and transient absorption experiments in solutions and glasses show rapid MS-CPET (3.2 × 1010 s-1 at 298 K). From 5.5 to 90 K, the reaction rate and kinetic isotope effect (KIE) are independent of temperature, with zero Arrhenius activation energy. From 145 to 350 K, there are only slight changes with temperature. This MS-CPET reaction thus occurs by tunneling of both the proton and electron, in different directions. Since the reaction proceeds without significant thermal activation energy, the rate constant indicates the magnitude of the electron/proton double tunneling probability.

Tailored photocleavable peptides: fragmentation and neutralization pathways in high vacuum.

Photocleavable tags (PCTs) have the potential for excellent spatio-temporal control over the release of subunits of complex molecules. Here, we show that electrosprayed oligopeptides, functionalized by a tailored ortho-nitroarylether can undergo site-specific photo-activated cleavage under UV irradiation (266 nm) in high vacuum. The comparison of UV photodissociation (UVPD) and collision-induced dissociation (CID) points to the thermal nature of the cleavage mechanism, a picture corroborated by the temperature dependence of the process. Two competing photodissociation pathways can be identified. In one case a phenolate anion is separated from a neutral zwitterion. In the other case a neutral phenol derivative leaves a negatively charged peptide behind. To understand the factors favoring one channel over the other, we investigate the influence of the peptide length, the nature of the phenolic group and the position of the nitro-group (ortho vs. para). The observed gas phase cleavage of a para-nitro benzylic ether markedly differs from the established behavior in solution.

Effect of nitrate, carbonate/bicarbonate, humic acid, and H2O2 on the kinetics and degradation mechanism of Bisphenol-A during UV photolysis.

In this study, the effects of natural water components (nitrate, carbonate/bicarbonate, and humic acid) on the kinetics and degradation mechanisms of bisphenol A (BPA) during UV-C photolysis and UV/H2O2 reaction were examined. The presence of NO3- (0.04-0.4 mM) and CO32-/HCO3- (0.4-4 mM) ions increased BPA degradation during UV photolysis. Humic acid less than 3 mg/L promoted BPA degradation, but greater than 3 mg/L of humic acid inhibited BPA degradation. During the UV/H2O2 reaction, all water matrix components acted as radical scavengers in the order of humic acid > CO32-/HCO3- > NO3-. All of the degradation reactions agreed with the pseudo-first-order kinetics. While eight byproducts (m/z = 122, 136, 139, 164, 181, 244, 273, 289) were identified in UV-C/NO3- photolysis reaction, four (m/z = 122, 136, 164, 244) and three byproducts (m/z = 122, 136, 164) were observed during UV-C/NO3-/CO32-/HCO3- and UV-C/CO32-/HCO3- reactions. Nitrogenated and hydrogenated byproducts were first observed during the UV-C/NO3- photolysis, but only hydrogenated byproducts as adducts were detected during the UV-C/NO3-/CO32-/HCO3- photolysis. Nitrogenated and hydrogenated byproducts were formed in the early stage of degradation by OH or NO2 radicals, and these byproducts were subsequently degraded into smaller compounds with further reaction during UV-C/NO3- and UV-C/NO3-/CO32-/HCO3- reactions. In contrast, BPA was directly degraded into smaller compounds by ß-scission of the isopropyl group by CO3-/HCO3 radicals during UV-C/CO32-/HCO3- reaction. Our results imply that the water components can change the degradation mechanism of BPA during UV photolysis.

Unexpected transformation of dissolved phenols to toxic dicarbonyls by hydroxyl radicals and UV light.

Water treatment systems frequently use strong oxidants or UV light to degrade chemicals that pose human health risks. Unfortunately, these treatments can result in the unintended transformation of organic contaminants into toxic products. We report an unexpected reaction through which exposure of phenolic compounds to hydroxyl radicals (•OH) or UV light results in the formation of toxic α,ß-unsaturated enedials and oxoenals. We show that these transformation products damage proteins by reacting with lysine and cysteine moieties. We demonstrate that phenolic compounds react with •OH produced by the increasingly popular UV/hydrogen peroxide (H2O2) water treatment process or UV light to form toxic enedials and oxoenals. In addition to raising concerns about potential health risks of oxidative water treatment, our findings suggest the potential for formation of these toxic compounds in sunlit surface waters, atmospheric water, and living cells. For the latter, our findings may be particularly relevant to efforts to understand cellular damage caused by in vivo production of reactive oxygen species. In particular, we demonstrate that exposure of the amino acid tyrosine to •OH yields an electrophilic enedial product that undergoes cross-linking reaction with both lysine and cysteine residues.

Bimetallic Au-Pd nanoparticles on 2D supported graphitic carbon nitride and reduced graphene oxide sheets: A comparative photocatalytic degradation study of organic pollutants in water.

Novel and sustainable bimetallic nanoparticles of Au-Pd on 2D graphitic carbon nitride (g-C3N4) and reduced graphene oxide (rGO) sheets was designed adopting an eco-friendly chemical route to obtain Au-Pd/g-C3N4 and Au-Pd/rGO, respectively. Elimination of hazardous pollutants, particularly phenol from water is urgent for environment remediation due to its significant carcinogenicity. Considering this aspect, the Au-Pd/g-C3N4 and Au-Pd/rGO nanocomposites are used as photocatalyst towards degradation of toxic phenol, 2-chlorophenol (2-CP) and 2-nitrophenol (2-NP) under natural sunlight and UV light irradiation. Au-Pd/g-C3N4 nanocomposite exhibited higher activity then Au/g-C3N4, Pd/g-C3N4 and Au-Pd/rGO nanocomposites with more than 95% degradation in 180 min under sunlight. The obtained degradation efficiency of our materials is better than many other reported photocatalysts. Incorporation of nitrogen atoms in the carbon skeleton of g-C3N4 provides much better properties to Au-Pd/g-C3N4 nanocomposite than carbon based Au-Pd/rGO leading to its higher degradation efficiency. Due to the presence of these nitrogen atoms and some defects, g-C3N4 possesses appealing electrical, chemical and functional properties. Photoluminescence results further revealed the efficient charge separation and delayed recombination of photo-induced electron-hole pairs in the Au-Pd/g-C3N4 nanocomposite. Generation of reactive oxygen species during photocatalysis is well explained through photoluminescence study and the sustainability of these photocatalyst was ascertained through reusability study up to eight and five consecutive cycles for Au-Pd/g-C3N4 and Au-Pd/rGO nanocomposites, respectively without substantial loss in its activity. Characterization of the photocatalysts after reaction signified the stability of the nanocomposites and added advantage to our developed photocatalytic system.

Gamma irradiation affects the total phenol, anthocyanin and antioxidant properties in three different persian pistachio nuts.

The effects of gamma irradiation (GR) on total phenol, anthocyanin and antioxidant activity were investigated in three different Persian pistachio nuts at doses of 0, 1, 2 and 4 kGy. The antioxidant activity, as determined by FRAP and DPPH methods, revealed a significant increase in the 1-2 kGy dose range. Total phenol content (TPC) revealed a similar pattern or increase in this range. However, when radiation was increased to 4 kGy, TPC in all genotypes decreased. A radiation dose of 1 kGy had no significant effect on anthocyanin content of Kale-Ghouchi (K) and Akbari (A) genotypes, while it significantly increased the anthocyanin content in the Ghazvini (G) genotype. In addition, increasing the radiation to 4 kGy significantly increased the anthocyanin content of K and G genotypes. To conclude, irradiation could increase the phenolic content, anthocyanin and antioxidant activity of pistachio nuts.

Persulfate enhanced photocatalytic degradation of bisphenol A by g-C3N4 nanosheets under visible light irradiation.

The enhancement of g-C3N4 photocatalytic degradation of bisphenol A (BPA) via persulfate (PS) addition was investigated under visible light irradiation. The effects of various parameters on the BPA degradation were investigated, such as catalysts dosage, PS concentrations, initial pH value and BPA concentration. The results showed that g-C3N4 nanosheets exhibited superior photocatalytic activity toward BPA degradation as compared with bulk g-C3N4. The addition of PS can further improve the g-C3N4 photocatalytic performance for BPA degradation. With 5 mM PS, the degradation rate of BPA was increased from 72.5% to 100% at 90 min, and the corresponding first-order kinetic constants were increased from 0.0028 to 0.0140 min-1. The removal efficiency of BPA increased with the decrease of solution pH value. The active radicals in the reaction system were tested by electron spin resonance (ESR) and radicals quenching experiments. Instead of persulfate radicals' oxidation, it was proposed that the main active radicals for BPA degradation were superoxide radicals and the photogenerated holes.